System and method of characterizing vascular tissue

ABSTRACT

A system and method is provided for using backscattered data and known parameters to characterize vascular tissue. Specifically, in one embodiment of the present invention, an ultrasonic device is used to acquire RF backscattered data (i.e., IVUS data) from a blood vessel. The IVUS data is then transmitted to a computing device and used to create an IVUS image. The blood vessel is then cross-sectioned and used to identify its tissue type and to create a corresponding image (i.e., histology image). A region of interest (ROI), preferably corresponding to the identified tissue type, is then identified on the histology image. The computing device, or more particularly, a characterization application operating thereon, is then adapted to identify a corresponding region on the IVUS image. To accurately match the ROI, however, it may be necessary to warp or morph the histology image to substantially fit the contour of the IVUS image. After the corresponding region is identified, the IVUS data that corresponds to this region is identified. Signal processing is then performed and at least one parameter is identified. The identified parameter and the tissue type (e.g., characterization data) is stored in a database. In another embodiment of the present invention, the characterization application is adapted to receive IVUS data, determine parameters related thereto (either directly or indirectly), and use the parameters stored in the database to identify a tissue type or a characterization thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 10/647,971,filed Aug. 25, 2003, which claims the benefit pursuant to 35 U.S.C.§119(e) of U.S. Provisional Patent Application Nos. 60/406,183, filedAug. 26, 2002, 60/406,254, filed Aug. 26, 2002, 60/406,148, filed Aug.26, 2002, 60/406,184, filed Aug. 26, 2002, 60/406,185, filed Aug. 26,2002, and 60/406,234, filed Aug. 26, 2002, all of which are incorporatedherein, in their entirety, by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to vascular tissue, or more particularly,to a system and method of using backscattered data and known parametersto characterize vascular tissue.

2. Description of Related Art

The present invention relates to the intra-vascular ultrasound (IVUS)analysis arts. It finds particular application to a system and methodfor quantitative component identification within a vascular objectincluding characterization of tissue. It should be appreciated thatwhile the present invention is described in terms of an ultrasonicdevice, or more particularly the use of IVUS data (or a transformationthereof) to characterize a vascular object, the present invention is notso limited. Thus, for example, using backscattered data (or atransformation thereof) to characterize any tissue type or compositionis within the spirit and scope of the present invention.

Ultrasonic imaging of portions of a patient's body provides a usefultool in various areas of medical practice for determining the best typeand course of treatment. Imaging of the coronary vessels of a patient byultrasonic techniques can provide physicians with valuable information.For example, the image data may show the extent of a stenosis in apatient, reveal progression of disease, help determine whetherprocedures such as angioplasty or atherectomy are indicated or whethermore invasive procedures may be warranted.

In a typical ultrasound imaging system, an ultrasonic transducer isattached to the end of a catheter that is carefully maneuvered through apatient's body to a point of interest such as within a blood vessel. Thetransducer may be a single-element crystal or probe that is mechanicallyscanned or rotated back and forth to cover a sector over a selectedangular range. Acoustic signals are then transmitted and echoes (orbackscatter) from these acoustic signals are received. The backscatterdata can be used to identify the type or density of a scanned tissue. Asthe probe is swept through the sector, many acoustic lines are processedbuilding up a sector-shaped image of the patient. After the data iscollected, an image of the blood vessel (i.e., an IVUS image) isreconstructed using well-known techniques. This image is then visuallyanalyzed by a cardiologist to assess the vessel components and plaquecontent.

Typically, the ultrasonic image data is transferred to a VHS videotape,digitized and then analyzed. This process, however, loses imageresolution since the videotape typically has a lower resolution than theoriginally collected backscatter data. Losing image resolution mayresult in an inaccurate evaluation of a vessel and its plaque content.Furthermore, certain image characteristics like brightness and contrastwill be different for different patients or could vary for the samepatient if the cardiologist varies the settings on the IVUS console. Theimages that are recorded on the videotapes are the same images viewed onthe IVUS console screen and, thus, subject to the settings on theconsole. Since plaque (or tissue type) is identified by its appearanceon the screen, errors may occur in the analysis if the screen settingshave been modified. Another drawback is that certain information (e.g.,tissue composition, etc.) cannot readily be discerned from an IVUS image(at least not to any degree of certainty). Thus, it would beadvantageous to have a system and method of characterizing and/orimaging a vascular object that overcomes at least one of thesedrawbacks.

SUMMARY OF THE INVENTION

The present invention provides a system and method of usingbackscattered data and known parameters to characterize vascular tissue.Embodiments of the present invention operate in accordance with anultrasonic device and a computing device comprising a characterizationapplication and a database. Specifically, the ultrasonic device (e.g.,intra-vascular ultrasound (IVUS) console and IVUS catheter) is used toacquire RF backscattered data (i.e., IVUS data) from a blood vessel. Forexample, a transducer may be attached to the end of a catheter andcarefully maneuvered through a patient's body to a point of interest.The transducer is then pulsed to acquire echoes or backscattered signals(i.e., IVUS data) reflected from the tissue of the vascular object. TheIVUS data is then transmitted to the computing device and used (eitherby the computing device or the IVUS console) to create an IVUS image.

In a first embodiment of the present invention, the characterizationapplication is adapted to receive and store characterization data (e.g.,tissue type data, etc.). Specifically, after the vascular object hasbeen interrogated, the vascular object is cross-sectioned for histology.The cross-section is then prepared with a fixing and staining processthat is well known in the art. The staining process allows a clinicianto identify a tissue type(s). The identified tissue type (e.g.,characterization data) is then provided to the characterizationapplication and stored in the database.

In another embodiment of the present invention, the characterizationapplication is further adapted to create a histology image and identifyat least one corresponding region on the IVUS image. In this embodiment,digitized data corresponding to the cross-sectioned vascular object isprovided to the characterization application. The digitized data is thenused to create a histology image. A region of interest (ROI) on thehistology image is then identified by the operator. Preferably, the ROIcorresponds to the characterization data, as previously provided. Thecharacterization application is then adapted to identify a correspondingregion on the IVUS image. To accurately match the ROI, however, it maybe necessary to warp or morph the histology image to substantially fitthe contour of the IVUS image. This warping removes histologicalpreparation artifacts caused by cutting the tissue. Accordingly, in oneembodiment of the present invention, the characterization application isfurther adapted to morph the histology image by (i) identifying (orreceiving identifying data from an operator on) at least one landmarkcommon to both the histology image and the IVUS image, (ii) use a firstalgorithm (e.g., a morphometric algorithm) to substantially align thecorresponding landmarks, and (iii) use a second algorithm (e.g., a thinplate spline (TPS) deformation technique) to substantially align thenon-landmark portions of the object.

In another embodiment of the present invention, the characterizationapplication is further adapted to determine and store parametersassociated with the ROI portion of the IVUS image. In this embodiment,the characterization application is adapted to identify the IVUS datathat corresponds to the ROI on the IVUS image. After the IVUS data hasbeen identified, and in accordance with one embodiment of the presentinvention, the characterization application is adapted to identify atleast one parameter of the IVUS data. In another embodiment of thepresent invention, the characterization application is adapted toidentify at least one parameter after frequency analysis has beenperformed (e.g., using fast Fourier transform, the Welch periodogram,autoregressive power spectrum (AR) analysis). The identified parameteris then stored in the database, where it is linked to thecharacterization data. This data (i.e., stored parameters andcharacterization data) can then be used to identify or characterizevascular tissue.

In a second embodiment of the present invention, the characterizationapplication is adapted to receive IVUS data, determine parametersrelated thereto, and use the parameters stored in the database (i.e.,histology data) to identify tissue type(s) or characterization(s)thereof. In this embodiment, the characterization application is adaptedto receive IVUS data from the IVUS console and identify at least oneparameter associated therewith (either directly or indirectly). In otherwords, the parameters may be identified directly from the IVUS data orfrom a transformation thereof (e.g., after frequency analysis). Theidentified parameters are then compared to the parameters stored in thedatabase (i.e., histology data). If a match (either exactly orsubstantially) is found, the related region is correlated to the tissuetype (or characterization) stored in the database. In one embodiment ofthe present invention, the characterization application is furtheradapted to display a reconstructed image of the interrogated vascularobject, where different tissue types are identified using differentcolors (e.g., discrete colors, gray-scales, etc.).

A more complete understanding of the system and method of usingbackscattered data and known parameters to characterize vascular tissuewill be afforded to those skilled in the art, as well as a realizationof additional advantages and objects thereof, by a consideration of thefollowing detailed description of preferred embodiments. Reference willbe made to the appended sheets of drawings which will first be describedbriefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a tissue-characterization system in accordance withone embodiment of the present invention, including an IVUS console, anIVUS catheter, a computing device and an input device.

FIG. 2 illustrates an exemplary IVUS image.

FIG. 3 illustrates a cross-section of an exemplary vascular objectin-vivo and in-vitro.

FIG. 4 illustrates an alternate embodiment of the computing devicedepicted in FIG. 1.

FIG. 5 illustrates an exemplary image of a characterized vascularobject.

FIG. 6 illustrates a method of characterizing a vascular object inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention operate in accordancewith an ultrasonic device and a computing device comprising acharacterization application and a database. In the detailed descriptionthat follows, like element numerals are used to describe like elementsillustrated in one or more figures.

FIG. 1 illustrates a tissue-characterization system 10 operating inaccordance with a first embodiment of the present invention. In thisembodiment, an intra-vascular ultrasound (IVUS) console 110 iselectrically connected to an IVUS catheter 120 and used to acquire RFbackscattered data (i.e., IVUS data) from a blood vessel. Specifically,a transducer 122 is attached to the end of the catheter 120 and iscarefully maneuvered through a patient's body to a point of interest.The transducer is then pulsed to acquire echoes or backscattered signalsreflected from the tissue of the vascular object. Because differenttypes and densities of tissue absorb and reflect the ultrasound pulsedifferently, the reflected data (i.e., IVUS data) can be used to imagethe vascular object. In other words, the IVUS data can be used (e.g., bythe IVUS console 110) to create an IVUS image. An exemplary IVUS image20 is provided in FIG. 2, where the light and dark regions indicatedifferent tissue types and/or densities. It should be appreciated thatthe IVUS console 110 depicted herein is not limited to any particulartype of IVUS console, and includes all ultrasonic devices known to thoseskilled in the art (e.g., a C-VIS Clearview Imaging System, etc.). Itshould further be appreciated that the IVUS catheter 120 depicted hereinis not limited to any particular type of catheter, and includes allultrasonic catheters known to those skilled in the art. Thus, forexample, a catheter having a single transducer (e.g., adapted forrotation) or an array of transducers (e.g., circumferentially positionedaround the catheter) is within the spirit and scope of the presentinvention.

Referring back to FIG. 1, the tissue-characterization system 10 furtherincludes a computing device 130 comprising a database 134 and acharacterization application 132 electrically connected to the database134 and adapted to receive IVUS data from the IVUS console 110. Itshould be appreciated that the database 134 depicted herein includes,but is not limited to, RAM, cache memory, flash memory, magnetic disks,optical disks, removable disks, SCSI disks, IDE hard drives, tape drivesand all other types of data storage devices (and combinations thereof,such as RAID devices) generally known to those skilled in the art. Itshould further be appreciated that the characterization application 132,as depicted and discussed herein, may exist as a single application oras multiple applications, locally and/or remotely stored. It should alsobe appreciated that the number and location of the components depictedin FIG. 1 are not intended to limit the present invention, and aremerely provided to illustrate the environment in which the presentinvention may operate. Thus, for example, a computing device having aplurality of databases and/or a remotely located characterizationapplication (either in part or in whole) is within the spirit and scopeof the present invention.

In one embodiment of the present invention, the characterizationapplication 132 is adapted to receive and store characterization data(e.g., tissue type, etc.). Specifically, after a vascular object hasbeen interrogated (e.g., IVUS data has been collected), a histologycorrelation is prepared. In other words, the vascular object isdissected or cross-sectioned for histology. In one embodiment of thepresent invention, the cross-section is previously marked, for examplewith a suture, so that the histology can be corresponded to a portion ofthe IVUS image. The cross-section is then prepared with a fixing andstaining process that is well known in the art. The staining processallows a clinician to identify a tissue type(s), or a chemical(s) foundwithin (e.g., a chemical corresponding to a particular tissue type,etc.). It should be appreciated that the particular method used toidentify or characterize the cross-sectional object is not a limitationof the present invention. Thus, all identification/characterizationmethods generally known to those skilled in the art are within thespirit and scope of the present invention.

The identified tissue type or characterization (i.e., characterizationdata) is then provided to the characterization application 132. In oneembodiment, as shown in FIG. 1, the characterization data is providedvia an input device 140 electrically connected to the computing device130. The characterization data is then stored in the database 134. Itshould be appreciated that the input device depicted herein includes,but is not limited to, a keyboard, a mouse, a scanner and all otherdata-gathering and/or data-entry devices generally known to thoseskilled in the art. It should further be appreciated that the termtissue type or characterization, as these terms are used herein,include, but are not limited to, fibrous tissues, fibro-lipidic tissues,calcified necrotic tissues, calcific tissues, collagen compositions,cholesterol, thrombus, compositional structures (e.g., the lumen, thevessel wall, the medial-adventitial boundary, etc.) and all otheridentifiable characteristics generally known to those skilled in theart.

In one embodiment of the present invention, the characterizationapplication is adapted to create a histology image and to identify atleast one corresponding region on an IVUS image. Specifically, digitizeddata is provided to the characterization application (e.g., via theinput device 140), where the digitized data corresponds to thecross-sectioned vascular object. The digitized data is then used tocreate a histology image (i.e., a digital image or outline thatsubstantially corresponds to the vascular object). A region of interest(ROI) on the histology image can then be identified by the operator.Preferably, the ROI is characterized by the characterization data, aspreviously provided, and may be the entire histology image or a portionthereof. The characterization application is then adapted to identify acorresponding region (e.g., x,y coordinates, etc.) on the IVUS image(i.e., the image created using the raw backscattered data, or the IVUSdata).

To accurately match the ROI, however, the histology image may need to bewarped to substantially fit the contour of the IVUS image. The warpingremoves histological preparation artifacts caused by cutting and/orfixing the tissue. For example, as shown in FIG. 3, the shape of ain-vivo vascular object 32 is generally round. Once this object is cut,or cross-sectioned for histology (i.e., creating an in-vitro vascularobject 34), the object may appear somewhat distorted, or flattened.Furthermore, the tissue may shrink (e.g., about 30%) when it is putthrough the fixation process. Thus, in order to identify a correspondingROI on the IVUS image, the histology image may need to be warped ormorphed, to return it to its original shape.

Accordingly, in one embodiment of the present invention, thecharacterization application is adapted to morph the histology image.Specifically, the characterization application is adapted to identify(or receive identifying data from an operator on) at least one landmarkcommon to both the histology image and the IVUS image (see e.g., FIG. 3,landmark A). The characterization application is then adapted to use (i)a first algorithm (e.g., a morphometric algorithm) to substantiallyalign the corresponding landmarks and (ii) a second algorithm (e.g., athin plate spline (TPS) deformation technique) to substantially alignthe non-landmark portions of the object. In other words, the secondalgorithm is used to shape the regions or boundaries between thelandmarks. It should be appreciated that-the landmarks discussed hereininclude, but are not limited to, side branch vessels, identifiableplaque or calcium deposits, and all other vascular tissue landmarksgenerally known to those skilled in the art.

In one embodiment of the present invention, the characterizationapplication is further adapted to determine and store parametersassociated with the ROI portion of the IVUS image. Specifically, thecharacterization application is adapted to identify the IVUS data (i.e.,the raw backscatter data) that corresponds to the ROI identified on theIVUS image. In other words, the IVUS data that was originally used tocreate the ROI on the IVUS image is identified. In one embodiment of thepresent invention, the characterization application is further adaptedto identify at least one parameter of the identified IVUS data. Thisparameter is then stored in the database, where it is linked to thecharacterization data. It should be appreciated, however, that eachparameter may be associated with more than one tissue type orcharacterizations. For example, a first parameter may be common tomultiple tissue types, thus requiring additional parameters to narrowthe field.

In another embodiment of the present invention, signal analysis (i.e.,frequency analysis, etc.) is performed on the identified IVUS databefore the parameters are identified. In other words, the IVUS data isconverted (or transformed) into the frequency domain (e.g., from thetime domain) to identify the frequency spectrum of the ROI. This isbecause the frequency information obtained from the backscattered signal(or parameters associated therewith) can serve as a “signature” for eachtissue type or characteristic. In one embodiment of the presentinvention, the frequency analysis is performed using a fast Fouriertransform (FFT). In another embodiment of the present invention, thefrequency analysis is performed using the Welch periodogram. In anotherembodiment of the present invention, the frequency analysis is performedusing autoregressive power spectrum (AR) analysis. At least oneparameter of the frequency-based signal is then identified and stored inthe database, where it is linked to the characterization data.

In another embodiment of the present invention, both backscattered data(e.g., IVUS data) and its frequency spectrum are analyzed to classifythe ROI portion of the IVUS image. Specifically, the frequency spectrum(or more particularly at least one parameter identified therefrom) isused to identify tissue type and the backscattered data is used toidentify tissue location. This is because the backscatter data is in thetime domain, and can thus be used to spatially identify certainfrequencies (or parameters related thereto). For example, if a vascularwall comprises multiple tissue layers, corresponding backscattered datacan be used to identify the location of these tissues and the relatedfrequency spectrum can be used to identify tissue types. It should beappreciated that, while certain embodiments have been described in termsof frequency transformation, the present invention is not so limited.Thus, alternate transformations (e.g., wavelet transformation, etc.) arewithin the spirit and scope of the present invention. It should furtherbe appreciated that the term parameter, as that term is used herein,includes, but is not limited to maximum power, minimum power,frequencies at maximum and/or minimum power, y intercepts (estimated oractual), slope, mid-band fit, integrated backscatter and all parametersgenerally known to (or discernable by) those skilled in the art. Itshould also be appreciated that the term “histology data,” as that termis used herein, includes data stored in the database (e.g.,characterization data, parameters, etc.).

One method of populating the database is illustrated in FIG. 6.Specifically, at step 610, IVUS data (i.e., RF backscatter data) iscollected from a portion of a vascular object. This data is then used tocreate an IVUS image at step 612. At step 614, the interrogated portionof the vascular object is cross-sectioned and a tissue type (or acharacterization thereof is identified. This information (i.e.,characterization data) is then transmitted to a computing device (or theequivalent thereof at step 616. At step 618, an image of thecross-sectioned vascular object is created and a ROI is identified(e.g., by an operator). This image is then morphed, if needed, tosubstantially match the cross-section image to the IVUS image at step620. This may include identifying at least one landmark and applying atleast one algorithm (e.g., a morphometric algorithm, a TPS deformationtechnique, etc.). At step 622, the ROI is mapped to the IVUS image andassociated IVUS data is identified. Spectral analysis is then performedon the associated IVUS data at step 624, and at least one parameter isidentified at step 626. The at least one parameter and thecharacterization data is then stored at step 628. In one embodiment ofthe present invention, the at least one parameter is stored such that itis linked to the characterization data. It should be appreciated thatthe order in which these steps are presented is not intended to limitthe present invention. Thus, for example, creating an IVUS image afterthe vascular object is cross-sectioned is within the spirit and scope ofthe present invention.

The above-described process is repeated for each tissue componentdesired to be identified and repeated for each component as many timesas desired in order to obtain a more accurate range of signalproperties. With the database populated, a tissue type or characteristiccan be automatically and accurately identified if the acquiredparameters substantially match parameters stored in the database.

Accordingly, in a second embodiment of the present invention, thecharacterization application is adapted to receive IVUS data, determineparameters related thereto, and use the parameters stored in thedatabase (i.e., histology data) to identify tissue type(s) orcharacterization(s) thereof. Specifically, with reference to FIG. 1, thecharacterization application 132 is adapted to receive IVUS data fromthe IVUS console 110. The characterization application 132 is thenadapted to identify at least one parameter associated (either directlyor indirectly) with the IVUS data. It should be appreciated that theIVUS data may either be received in real-time (e.g., while the patientis in the operating room) or after a period of delay (e.g., via CD-ROM,etc.). It should further be appreciated that the identified parametersshould be related (generally) to the stored parameters. Thus, forexample, an estimated Y intercept parameter should be identified if datarelated to a signal's estimated Y intercept is stored in the database134 and linked to at least one tissue type. Moreover, if the storedparameters were acquired after frequency analysis was performed (i.e.,are related to a frequency-based signal), then frequency analysis(preferably of the same type) should be performed on the IVUS databefore parameters are identified. However, the IVUS data may be used toidentify spatial information, as previously discussed.

The identified parameters are then compared to the parameters stored inthe database (i.e., histology data). If a match (either exactly orsubstantially) is found, the related region is correlated to the tissuetype (or characterization) stored in the database 134 (e.g., as linkedto the matching parameters). It should be appreciated that a match mayoccur as long as the parameters fall within a range of properties for aparticular tissue type found in the database.

In one embodiment, after each region is identified, the characterizationapplication is further adapted to display a reconstructed image of theinterrogated vascular object on a display. A computing device 130including such a display 136 is illustrated in FIG. 4. In one embodimentof the present invention, each tissue type (or characterization) isdistinguished through the use of gray-scales or discrete colors. Forexample, FIG. 5 illustrates an exemplary reconstructed vascular object510, where different tissues (e.g., calcific tissues 512, fibroustissues 514, calcified necrotic tissues 516 and fibro-lipidic tissues518) are identified using different shades of gray. Such a system makesdifferent tissue types or characterizations easily identifiable.Additional examples of characterized vascular objects are provided byU.S. Pat. No. 6,200,268, which was issued on Mar. 13, 2001, and isincorporated herein, in its entirety, by reference. It should beappreciated that the reconstructed vascular object may further identifyvascular borders. Systems and methods of identifying vascular bordersare provided by U.S. Provisional Application Nos., 60/406,184,60/406,234, and 60/406,185, which were filed Aug. 26, 2002, and by U.S.Pat. No. 6,381,350, which issued Apr. 30, 2002, and are incorporatedherein, in their entirety, by reference.

Having thus described embodiments of a system and method of usingbackscattered data and known parameters to characterize a vasculartissue, it should be apparent to those skilled in the art that certainadvantages of the system have been achieved. It should also beappreciated that various modifications, adaptations, and alternativeembodiments thereof may be made within the scope and spirit of thepresent invention. The invention is further defined by the followingclaims.

1. A method of characterizing vascular tissue, comprising: obtaining anintra-vascular ultrasound (IVUS) signal, said IVUS signal comprising RFdata backscattered from vascular tissue; transforming said IVUS signalinto at least one other domain; identifying a plurality of parameters ofsaid transformed signal; and using said plurality of parameters andpreviously stored histology data to characterize at least a portion ofsaid vascular tissue.
 2. The method of claim 1, wherein said step oftransforming said IVUS signal further comprises transforming said IVUSsignal from the time domain into the frequency domain.
 3. The method ofclaim 1, wherein said step of transforming said IVUS signal furthercomprises performing a wavelet transformation on said IVUS signal. 4.The method of claim 2, wherein said step of transforming said IVUSsignal further comprises processing said identified portion of said IVUSsignal using a fast Fourier transform (FFT).
 5. The method of claim 2,wherein said step of transforming said IVUS signal further comprisesprocessing said identified portion of said IVUS signal using the Welchperiodogram.
 6. The method of claim 2, wherein said step of transformingsaid IVUS signal further comprises processing said identified portion ofsaid IVUS signal using autoregressive power spectrum (AR) analysis. 7.The method of claim 1, wherein said step of identifying a plurality ofparameters further comprises identifying at least two parametersselected from a group consisting of maximum power, minimum power,frequency at maximum power, frequency at minimum power, y intercept,slope, mid-band fit, and integrated backscatter.
 8. The method of claim1, further comprising transmitting acoustic signals within a vascularobject and at least toward said vascular tissue.
 9. The method of claim1, wherein said step of using said plurality of parameters andpreviously stored histology data to characterize at least a portion ofsaid vascular tissue further comprises using said plurality ofparameters and said previously stored histology data to identify atissue type of said at least a portion of said vascular tissue, saidtissue type being selected from a group consisting of fibrous tissues,fibro-lipidic tissues, calcified necrotic tissues, and calcific tissues.10. The method of claim 9, further comprising imaging said at least aportion of said vascular tissue on a display.
 11. The method of claim10, wherein said step of imaging said at least a portion of saidvascular tissue further comprises using a particular color to identifysaid tissue type of said at least a portion of said vascular tissue. 12.The method of claim 10, wherein said step of imaging said at least aportion of said vascular tissue on a display further comprises usingsaid IVUS signal to identify a location of said tissue type on saiddisplay.
 13. A method of characterizing a vascular object, comprising:providing a classification table comprising a plurality of tissue typesand corresponding characteristics; acquiring an intra-vascularultrasound (IVUS) image; selecting a region of the IVUS image;identifying a plurality of parameters corresponding to said region ofsaid IVUS image; using said plurality of parameters and saidclassification table to determine a tissue type corresponding to saidregion of said IVUS image; and applying a color scheme to said tissuetype, said color scheme being used to differentiate between differenttissue types once displayed.
 14. The method of claim 13, furthercomprising performing frequency analysis on IVUS data corresponding tosaid region of said IVUS image before said plurality of parameters areidentified, said frequency analysis being performed using a fast Fouriertransform (FFT).
 15. The method of claim 13, further comprisingperforming frequency analysis on IVUS data corresponding to said regionof said IVUS image before said plurality of parameters are identified,said frequency analysis being performed using a Welsh periodogram. 16.The method of claim 13, further comprising performing autoregressivepower spectrum (AR) analysis on IVUS data corresponding to said regionof said IVUS image before said plurality of parameters are identified.17. The method of claim 13, further comprising performing a wavelettransformation on IVUS data corresponding to said region of said IVUSimage before said plurality of parameters are identified.
 18. A methodfor generating a tissue map, comprising the steps of: obtaining anintra-vascular ultrasound (IVUS) signal; transforming the IVUS signalinto the frequency domain; analyzing the signal based on at least twoparameters selected from the group consisting of maximum power, minimumpower, frequency at maximum power, frequency at minimum power, yintercept, slope, mid-band fit, and integrated backscatter; andclassifying the tissue properties based on matching the analyzed datawith a database.
 19. The method of claim 18, wherein said step oftransforming the IVUS signal into the frequency domain further comprisesprocessing the IVUS signal using a Welsh periodogram.
 20. The method ofclaim 18, wherein said step of transforming the IVUS signal into thefrequency domain further comprises processing the IVUS signal usingautoregressive power spectrum (AR) analysis.